This invention relates to certain polymeric pH-sensitive optical filter agents and to articles or products including such agents. More particularly, it relates to certain transparent (or substantially non light-absorbing) polymeric materials which are adapted upon contact with alkali to the provision of substantial light-absorbing or opacification functionality.
Various patents, including, among others, U.S. Pat. No. 3,752,692 (issued Aug. 14, 1973 to R. W. Young) and U.S. Pat. No. 3,794,485 (issued Feb. 26, 1974 to S. M. Bloom et al.) describe photographic film units which, after being exposed within a camera, are designed to be removed from the camera for processing. Since a photosensitive element remains light-sensitive during the processing operation, which typically is effected in an alkaline processing composition, one or more opaque layers will generally be provided in the film unit to afford protection of the photosensitive material against further exposure (fogging) by actinic light. Thus, in the aforesaid U.S. Pat. No. 3,752,692, there is disclosed a film unit including a support having thereon an opaque layer comprising dispersed carbon black. In the aforesaid U.S. Pat. No. 3,794,485, there is described a film unit having a layer of dye precursor material which upon contact with aqueous alkaline processing composition forms a colored species to prevent photoexposure when the film unit is removed from a camera for processing. In U.S. Pat. No. 4,269,925 (issued May 26, 1981 to D. H. R. Barton et al.) certain polymeric pH-sensitive optical filter agents having hydrazone moieties are described for application in photoexposed photosensitive elements against the occurence of fogging during in-light development.
It will be appreciated that for certain applications, notably in the production of photographic products, it will be advantageous to provide a layer of transparent (substantially non light-absorbing) polymeric material which can be, as desired, converted to a colored or light-absorbing form capable of providing opacification functionality.